Even accepting all your figures, they total £19.23bn. That's your absolute theoretical maximum, assuming you could eliminate every penny of that spending, which you obviously couldn't.
You've also mixed up entirely different budgets, overstated asylum accommodation costs and potentially double-counted expenditure.
More importantly, you've provided no evidence that those savings would be sufficient to meet whatever budgetary target you're talking about, let alone address the longer-term growth in pension expenditure.
Nobody is saying pensioners must have their benefits cut. The point is that pension spending represents an enormous proportion of welfare expenditure, and listing three unrelated areas of spending doesn't make that arithmetic disappear.
You've demonstrated where you'd prefer to cut spending, not that your proposals eliminate the need to examine pensions.